Welcome to Anna's G Research Site
Overview of Our Research
The release of gas molecules from the crystal lattice is distinctive for each compounds. For example, some crystals tolerate a build-up of large gas bubbles within the crystals before cracking, whereas others release gas concurrently with light exposure. Some crystals shatter fiercely upon exposure to light, whereas others leap around and gradually break apart. We are elucidating how the crystal packing arrangement affect the release.
Solid State Photochemistry
Solid-state photoreactions generally progress with minimal molecular movement due to the rigidity of the crystal lattice. The restricted motions within crystals render solid-state reactions markedly more selective than their counterparts in solution. By obtaining X-ray crystal structures of the reactant and product, it is possible to establish structure-reactivity relationships as the reactant and the product are forced into consistent geometry within the crystals. Our knowledge of solid-state reaction mechanisms is generally limited to structure-reactivity correlations, which unfortunately excludes many critical details of the mechanism. For example, photoreactions that yield radicals such as triplet nitrenes and biradicals within crystal lattices make it possible to selectively form new carbon-carbon and carbon-nitrogen bonds. However, structure-reactivity correlations do not allow the characterization of these intermediates or their precursors or make it possible to acquire the kinetics of the solid-state reactions. This limited knowledge of the reaction mechanisms in crystals is one of the main factors that have impeded further development in using crystals to carry out selective bond formations from radicals.
Recent findings have shown that nanocrystals in water suspension, with sizes smaller than the wavelength of excitation, are suitable for laser flash photolysis. We have demonstrate that we can detect triplet nitrenes and biradicals directly within crystals, thus making it possible to correlate the solid-state kinetics with the crystal structure and reveal the solid-state reaction mechanisms in detail.
Photoremovable Protecting Groups
In the past decade a series of useful molecular systems known as phototriggers, photoswitches, photocaging groups, or photoremovable protecting groups (PRPGs) have been used in a wide variety of applications, including the release of fragrances from household goods, as an aid in multi-step synthesis, and in drug and gene delivery. PRPGs also make it possible for biochemists to release bioactive compounds in living tissue with both high temporal and spatial accuracy, thus making it possible to study physiological events such as enzyme activity, ion channel permeability, and muscle contraction by ATP hydrolysis. The choice of PRPG is critical, depends on the system under investigation, and must be tailored to the application. Thus, there is a need for new PRPGs that can satisfy the diverse requirements of numerous applications.
We have designed several new photoprotecting groups and studied the mechanism for the photorelease. Understanding the reaction mechanism for the photorelease has allowed us to design the next generation of PRPGs that can be tailored towards specific applications. Currently, we are using radicals and radical rearrangement along with intramolecular H-atom bonding to achieve photorelease in high quantum yields and to control the rate of release.
Triplet Alkyl- & Vinylnitrenes
Organic azides are one of the more adaptable functional groups in synthetic chemistry because they react easily with both electrophiles and nucleophiles to form new C–N bonds. The dipolar character of organic azides makes them suitable for cycloaddition to alkynes and olefins, which has been used in countless syntheses. The quest for sustainable chemistry has inspired interest in using sunlight, a natural resource, or energy-efficient light-emitting diodes (LEDs) for synthetic applications.
Generally, the photochemistry of organic azides has been of limited synthetic utility, as their reactivity is complex and depends on multiple factors, such as molecular structure and whether excitation occurs directly or with sensitizers. Upon excitation, organic azides can form products in a concerted manner or form nitrene intermediates, and their reactivity depends on their electron configuration and substituents.
Triplet sensitization of aryl- and vinyl azides has been successfully used for selective C–N bond formation. We are working towards characterizing and determining the factors that control the reactivity of triplet vinylnitrenes.